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a=xqWC_Br6kY4A:10 a=IkcTkHD0fZMA:10 a=Yq5XynenixoA:10 a=GoEa3M9JfhUA:10 a=VkNPw1HP01LnGYTKEx00:22 a=jiCTI4zE5U7BLdzWsZGv:22 a=EIcjfB9IiI4px24ztqRk:22 a=ROK7AcxOToVZeOjc18MA:9 a=3ZKOabzyN94A:10 a=QEXdDO2ut3YA:10 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwMzE3MDEyNCBTYWx0ZWRfX0I+gRZKyt3TS yAq22XrqQa/R6IFRKfeRynI7Dol4UPyBB8EVeld+owk6tV+8j4wvF3wqeQlp+Jg0szhYyRqQWe4 TpuPPHlanLEC+ZWNwQJflzrqRD8hZ+SQcWSUktmvKjcpXbx1aR7sPCJ4FkPCNxKZUm0U341SkQL ib88Ycbgg8ntgmwRQBWzB5NZp+u57E2u/955dS8iIm2o5QCRrbO5yJVUSBCfwYCrvGPVzvhje5+ HbWTBlBMTn2XT4Dxf4oYhsPYwcAlyY8nuw/8tIV4noHkeBlZEzyeSsVypBcpNVuxh622uRzR42q OpFHJyJLJy3mywD4rHN8P+mlEEGneIbuFAmoKnuSjuOBpzc2ZmdyK2GrmOejIH+EyuC4NXU4inK OiJpKeMs/Yf/WK3R/dbSr7CNpJ1yNDubmKhWcoEvQHE+X/LJ4c8Iuw39S+aq4FInPlPMmOQA2+P fu+PHRgGFNpwJv1P9Pg== X-Proofpoint-GUID: LxnWP0tvjIrVCiWexfvBMChQQsq7wqmA X-Proofpoint-ORIG-GUID: LxnWP0tvjIrVCiWexfvBMChQQsq7wqmA On 3/17/26 7:32 AM, Breno Leitao wrote: > Hello Tejun, > > On Fri, Mar 13, 2026 at 07:57:20AM -1000, Tejun Heo wrote: >> Hello, >> >> Applied 1/5. Some comments on the rest: >> >> - The sharding currently splits on CPU boundary, which can split SMT >> siblings across different pods. The worse performance on Intel compared >> to SMT scope may be indicating exactly this - HT siblings ending up in >> different pods. It'd be better to shard on core boundary so that SMT >> siblings always stay together. > > Thank you for the insight. I'll modify the sharding to operate at the > core boundary rather than at the SMT/thread level to ensure sibling CPUs > remain in the same pod. > >> - How was the default shard size of 8 picked? There's a tradeoff >> between the number of kworkers created and locality. Can you also >> report the number of kworkers for each configuration? And is there >> data on different shard sizes? It'd be useful to see how the numbers >> change across e.g. 4, 8, 16, 32. > > The choice of 8 as the default shard size was somewhat arbitrary – it was > selected primarily to generate initial data points. Perhaps instead of basing the sharding on a particular number of CPUs per shard, why not cap the total number of shards? IIUC that is the main concern about ballooning the number of kworker threads. > I'll run tests with different shard sizes and report the results. > > I'm currently working on finding a suitable workload with minimal noise. > Testing on real NVMe devices shows significant jitter that makes analysis > difficult. I've also been experimenting with nullblk, but haven't had much > success yet. > > If you have any suggestions for a reliable workload or benchmark, I'd > appreciate your input. > >> - Can you also test on AMD machines? Their CCD topology (16 or 32 >> threads per LLC) would be a good data point. > > Absolutely, I'll test on AMD machines as well. > > Thanks, > --breno -- Chuck Lever